In a wide variety of commonly employed dual chamber pacing modalities, cross-talk could cause one or more errors. For example, a paced atrial event may be sensed by a ventricular lead and misinterpreted as a ventricular event. This would effectively be far field sensing of an atrial pace. This typically would not be a problem with intrinsic atrial depolarizations, due to their lower magnitude. Conversely, far field sensing of intrinsic R waves or paced ventricular events could likewise be misinterpreted if sensed by an atrial lead.
To account for such errors, various blanking or refractory periods are employed such that these events are either not sensed or are simply ignored. In dealing with far field sensing of atrial-paced events, ventricular events that are sensed during a given window following the atrial pace are ignored. Depending upon the application, this window may be referred to as the atrial blanking period (ABP) or some similar nomenclature. Through clinical application, practitioners have determined that if such far field sensing is going to occur, it typically happens within 80 ms or less of the original event (e.g., the atrial pace). Thus, this window is conservatively set at 80 ms or so, depending upon the specific device or the manufacturer.
In use, such as in a DDD mode, providing this window adequately addresses the cross-talk problem and generally does not create additional problems. Sometimes genuine intrinsic events will occur during the window and will also be ignored. For example, a premature ventricular contraction (PVC) is an intrinsic, conducted event but if it falls within the window it will be ignored.
Whether a far field sense or an intrinsic event, such as a PVC, occurs and is ignored, the subsequent action of the device in typical dual chamber modes is to provide a ventricular pace at the expiration of a predetermined interval following the initial atrial event, unless inhibited. If the ignored event was cross talk, it is certainly possible that a subsequent intrinsic ventricular event will occur and inhibit the pace. Alternatively, for any number of reasons no intrinsic event will occur during the atrial-ventricular interval (AVI) and the ventricular pace is delivered. If the ignored event was a PVC, it is quite likely that there will not be another intrinsic ventricular event in the current A-A interval and the device will deliver a pacing pulse at the expiration of the AVI.
Thus, the use of such a window in dual chamber devices is appropriate to prevent cross talk without introducing additional problematic results. As disclosed in the above referenced applications, a mode and/or protocol is provided that minimizes or greatly reduces ventricular pacing and is referred to as MVP. In summary, MVP tolerates a complete cycle (A-A) interval without ventricular activity, in order to promote intrinsic conduction. In many patients, the conduction pathway is intact but is delayed beyond the capabilities of traditional dual chamber mode timing. Thus, ventricular pacing is provided when not absolutely necessary and this is believed to be undesirable.
Various embodiments of MVP are described in greater detail in the referenced applications, but the mode generally operates by monitoring a complete cycle for intrinsic conduction. If intrinsic conduction fails and no ventricular event occurs, ventricular pacing is provided in the subsequent cycle.
The use of the above described window (ABP) presents a challenge to this minimized or reduced ventricular pacing mode. For example, if true cross talk occurs and is ignored, subsequent operation continues unhindered. However, if a PVC occurs during this window, it is ignored. Thus, a true intrinsic ventricular event is being ignored by a mode that bases it subsequent operation on the presence or absence of intrinsic ventricular activity during a given cycle. If a PVC occurs during this window it is ignored; assuming no other ventricular activity occurs during this interval, which is quite possible, the device determines that the current A-A interval is devoid of intrinsic ventricular conduction. Subsequently, the device mode switches or otherwise operates to deliver ventricular pacing in a subsequent cardiac cycle and depending upon the embodiment, one or more subsequent cycles. While not in and of itself harmful, this ventricular pacing is generally not necessary as intact conduction exists. As a result, PVC's may operate to reduce the efficiency of the ventricular minimization or reduction protocol insomuch as that efficiency is determined to be the reduction or elimination of otherwise unnecessary ventricular pacing. This may simply result in a relatively low number of unnecessary ventricular paces. Alternatively, depending upon the specific embodiment of MVP, a series of PVCs may be interpreted as a loss of conduction that prevents a return to the atrial based mode for a longer period of time.